Outline

Plectin is a ubiquitous multifunctional cytolinker protein expressed at high levels in muscle and skin. The most common disease caused by plectin deficiency, epidermolysis bullosa simplex (EBS)-MD, is characterized by muscular dystrophy and severe skin blistering. EBS-MD patients and plectin-deficient mice display massive desmin aggregation, misalignement of Z-disks, and mitochondrial dysfunction – the hallmarks of myofibrillar myopathies (MFM). As the ubiquitin-proteasome and the autophagic-lysosomal systems are responsible for the degradation of misfolded proteins and protein aggregates, disturbances of protein quality control may also play an important role in plectin-deficient tissue. To analyze the mechanistic link between desmin network collapse and protein aggregation due to plectin deficiency, intermediate filament networks were assessed in whole muscle and teased muscle fibers derived from muscle-fiber restricted (MCK-Cre) conditional plectin knockout mice. Moreover, to investigate the pathogenesis of plectin-related MFM at the single-cell level, immortalized (p53-/-) wild-type and plectin-deficient myocyte cell lines were established. Myoblasts of this type were able to fuse and form multinucleated myotubes in culture. Myotubes developed a contractile apparatus and formed Z-disks, showing spontaneous contractions after a week of differentiation. When compared to myofibers obtained by teasing apart whole muscle ex vivo, differentiated myotubes closely resembled mature structures. Most importantly, plectin-deficient myocytes spontaneously develop desmin aggregates when differentiated into contractile myotubes, thus closely mimicking the plectin-related MFM phenotype ex vivo. This system opens the door to cell biological/biochemical analyses of plectin-related MFM including live cell imaging. Moreover, these plectin-deficient myoblasts will also provide the scientific basis for the development of novel treatment concepts for plectinopathy patients, as they can be easily treated with potential therapeutics. In fact, when myoblasts were treated with chemical chaperones during differentiation, plectin-related MFM pathology was ameliorated in plectin-deficient myotubes.